1. Field of the Invention
The present invention relates to a device for performing immunoassay and, more particularly, to an immunoassay device for simultaneously performing various types of immunoassay and a method of performing immunoassay using the device.
2. Description of the Prior Art
Immunoassay is a method of identifying or quantifying antigens or antibodies by utilizing high specificity and detection sensitivity in antigen-antibody reactions. In order to quickly, easily perform immunoassay, various types of devices are proposed. A simplest device is a test piece carrying one immunoassay reagent, i.e., an antibody or antigen on a strip-like support. Such a test piece performs only one type of immunoassay in each test.
In cell-typing for identifying histocompatibility, at least eighty different immunoassay tests are required. In order to simultaneously perform such a multi-test immunoassay the following conventional immunoassay device is proposed.
U.S. Pat. No. 4,591,570 describes an immunoassay device having small immunoreaction regions, i.e., small regions applied with immunoassay reagents, aligned with high density on a flat plate such as a glass or plastic cover slip. More specifically, in this device, a plurality of immunoassay reagent solutions (e.g., antibody solutions) are applied to the flat plate surface in a given sequence to form dots each having a diameter of 0.25 to 1 mm, and the immunoassay reagents are fixed by adsorption or chemical bonding to the flat plate surface. By using this immunoassay device, various immunoassay tests can be simultaneously performed.
A cell suspension as a specimen is dripped on all immunoreaction regions and different antigen-antibody reactions occur in the individual immunoreaction regions. Cell surface antigens are selectively and specifically bound with an antibody in each immunoreaction region. Therefore, by detecting the presence/absence of bonding of cells to all the immunoreaction regions and the number of cells bonded to these regions, cell-typing and a content ratio of cells to the corresponding cell suspension can be determined.
The conventional immunoassay device described above has the following disadvantages.
First, it is difficult to form small immunoreaction regions. When immunoassay reagent solutions are dripped on predetermined small regions on the flat plate surface, no marks are formed on the positions to be applied with the reagent solutions. In addition, different immunoassay reagent solutions must be applied to the predetermined areas without mixing and this operation is very difficult. It is also difficult to set the immunoreaction regions having an identical area.
Second, it is difficult to control the amount of immunoassay reagent fixed to each region on the plate surface. The amount of immunoassay reagent applied to the plate surface varies depending on the concentration of the solution applied to the plate surface, the type of reagent, and the material of the plate. In order to control the amount of immunoassay reagent, it is necessary to increase or decrease an amount of reagent solution. The reagent solution dripping on the plate surface is kept in a predetermined area of the plate surface by a surface tension. Thus, the amount of reagent solution kept in the predetermined area is limited by only the surface tension. It is, therefore, almost impossible to increase the amount of reagent solution in a predetermined area. This disadvantage also occurs in dripping of a specimen solution.
The third disadvantage is associated with a practical application to the immunoassay. Since the device has a plate with a flat surface, the specimen solution applied to the flat plate surface flows over the entire surface and may overflow. If the specimen is obtained from blood of a patient having an infectious disease, a secondary infection may be caused. When a plurality of specimens are applied to a single plate, they are mixed. Therefore, a plurality of specimens cannot be analyzed on a single plate.
A conventional example free from the above disadvantages is disclosed in U.S. Pat. No. 4,154,795. In this immunoassay device, wells having the same area are arranged in an 8.times.12 matrix on a surface. When this device is used, an immunoassay reagent is fixed within the inner wall surface of each well or added in it. A specimen is added to each well to cause a specific antigen-antibody reaction between the specimen and the immunoassay reagent, thereby detecting an antigen or antibody existing in the sample.
The immunoreaction region is distinctly defined by each well in the conventional immunoassay device of a well type, and the problems posed by the above conventional immunoassay devices of flat plate type can be solved. However, washing required in the immunoreaction test is very cumbersome. In order to fix an immunoassay reagent within a well region defined by the inner walls, an excess reagent must be washed after the reagent is applied to the matrix surface. A blocking agent is added to prevent nonspecific adsorption for the fixed immunoassay reagent. Washing is also required to remove any excess blocking agent and requires a cumbersome operation for supplying a washing solution (a buffer solution) into each well and removing the solution from each well, thus resulting in time-consuming operation and requiring much labor.